The invention relates to a heated gas sample transfer line from a gas chromatograph (GC) to an ion source of a mass spectrometer (MS). Various combinations for coupling of gas chromatographs (GC) with mass spectrometers (MS) are known in the art. In the GC, samples are injected onto a GC column through an injection port and become separated while passing through the GC column. The effluent of the GC column is conveyed from the GC oven to the ion source of the MS within a column extension of a transfer line. In the ion source, the sample molecules are ionized, for example by electron impact or chemical ionization, before being analyzed according to their mass-to-charge ratios.
During the transfer of the effluent from the GC column oven to the ion source, it is necessary to maintain a uniform temperature along the column extension. If a significant temperature gradient exists so that the temperature varies at different points along the column extension, cold spots may occur to cause condensation from the gas phase of the sample so that it will either not be passed through to the MS or will exhibit excessive chromatographic peak broadening or peak tailing. On the other hand, hot spots that appear may cause some compounds to degrade thermally with a resultant change in their chemical structure. Similar effects can occur even if the transfer line is at uniform temperature if the temperature of the transfer line is either too cold or too hot during the elution of any given chemical compound. Additionally, excessive temperatures of transfer line can lead to elevated “chemical noise” and lower signal-to-noise ratio for any given analytical results. Temperature variations along the length of the transfer line of +/−10° Celsius are generally acceptable, although variations of less than +/−5° Celsius are required in some applications.
Usually, GC-MS transfer lines are rigidly attached to the housing of the mass spectrometer and provide a uniform temperature environment on the column extension when column effluents are conveyed through the walls of the GC oven and the mass spectrometer into the ion source.
MS ion sources have to be cleaned in regular periods, or the filaments for electron generation have to be replaced. For these maintenance operations, the ion sources have to be taken out of the MS housing. Generally, they are mounted with fasteners that are sometimes hard to access, require clean tools and potentially can be lost inside the instrument. In addition, the column extension has to be removed from the transfer line, and the transfer line has to be disconnected from the ion source, always with a risk to damage the GC column or the column extension, respectively.